The tanning of leather is a complex process described, for instance, in the Kirk-Othmer Encyclopedia of Chemical Technology. Fourth Edition, Volume 15, pp. 159–176. The vegetable, inorganic, and synthetic tanning processes are described in a review “Practical leather Technology, T. C. Thorstensen (4th Ed., 1993, Krieger Publishing Company, Malabar Fla.). Produced from animal skins, leather is used for many purposes, including shoes, upholstery, clothing, gloves, hats, books, sports equipment, and the like. In most such uses, water repellency is desired and conventionally achieved by the application of fats, or by surface treatment of the leather after drying. For example, various hydrophobes, such as silicone treatments and fluorinated esters, have been applied to leather to provide water repellency. Silicones, while hydrophobic, are oleophilic and thus, while providing water repellency, tend to increase soiling.
A number of treatment processes have been described for improving the water- and oil-repellency of leather, for instance, Diesenroth, et al, in U.S. Pat. No. 5,693,747 describe sulfur-containing diols capable of being reacted with urethanes to make repellent materials. Del Pesco et al., in U.S. Pat. No. 6,479,612, describe a polymer having at least one urea linkage derived by contacting (1) at least one polyisocyanate, or mixture of polyisocyanates, (2) at least one fluorocarbon alcohol, fluorocarbon thiol or fluorocarbon amine, (3) at least one straight or branched chain alcohol, amine or thiol, and (4) at least one alcohol containing a sulfonic acid group or its salt, and then (5) optionally at least one linking agent useful for imparting oil repellency and water repellency to substrates. However, these compositions do not address soil resistance.
The cleaning of such conventionally produced leathers can be difficult or impossible because leathers made by conventional tanning processes do not stay soft and compliant when wetted with water or water- based solutions of the type used for washing traditional woven fabrics. Instead, when wetted, leather products exhibit a tendency to become stiff and/or brittle as they dry with cracks or splits often occurring. As a result, cleaning techniques for leather have generally been limited. Some leather may be cleaned by relatively costly dry cleaning processes employing organic solvents. Recent tanning processes, such as that of U.S. Pat. No. 5,972,037 of Scheen, produce machine washable and machine dryable leather cleanable in typical household appliances. For all leathers, resistance to soiling and staining would improve ease in caring for the leather.
Therefore, it is desirable to provide a method of imparting soil resistance to leather. Furthermore, it is desirable that the treatment agents employed be effective with essentially no changes in the leather processing and tanning steps, be compatible with leather treatment bath formulations, and be applied without the need for additional equipment. The present invention provides such a method.